Microwave radiometers and Remote Sensing: Windsat Global monthly average Sea Surface Temperature (SST) for 2014

Microwave radiometers are passive sensors that receive microwave radiation naturally emitted by the environment. The strength and the wavelength of the radiation is fundamentally a function of the temperature and emissivity of the target. The microwave radiometry works under the principle that all bodies at non-zero Kelvin temperature ( -273.15 degrees Celsius) emit electromagnetic radiation. The microwave region spreads across 1 mm to 1 m of the electromagnetic spectrum.

Compared to visible optical and infrared sensors, the microwave radiometers have the advantage, specially on the lower part of the spectrum, to pass through the atmosphere and be able to sense the surface of the Earth, in fact, with low soil moisture content, they can penetrate the soil ~10cm. On the other side, their spatial resolution is quite poor ~50 km making them appropriate for global analysis but not regional ones.

A microwave radiometer consists of an antenna that observes a path. The signal gathered by it is filtered and amplified, and then displayed as digital data. A radiometer aboard a satellite can then be used to measure electromagnetic emissions coming from the atmosphere or the Earth's surface: water vapour, cloud liquid water, rain rate, sea surface temperature, soil moisture and ice and snow characteristics.

The Windsat is a radiometer capable to measure the sea surface temperature (SST). It was launched on 2003 aboard the U.S, Department of Defense Coriollis₁ satellite which is on a

near-polar orbit at an altitude of 840 km. The local ascending node is at 6pm and the common swath width is approximately 950 km.

A sample of 2014's Global Average Sea Surface Temperature (SST) is presented, specifically the monthly average Global Sea Temperature of the months of March and September (images 1-2) and a video composition of the whole of 2014 Average SST by month. Observing the images, apart from the changes of the SST by latitude, one can notice a maximum ice shelf at the Arctic in March vs. a minimum in Antarctica and vice versa in September. In the video, the SST variations on the two hemispheres are represented. Also the changes at the shelf ice of the Arctic and Antarctica are perfectly noticeable.

1.WindSat was meant to demonstrate the capabilities to measure the ocean surface wind vector from space, a key parameter for short-term weather forecasting, the issuing of timely weather warnings, and the gathering of general climatological data. In addition, it affects a broad range of naval missions, including strategic ship movement and positioning, aircraft carrier operations, aircraft deployment, effective weapons use, underway replenishment, and littoral operation.

Image 1. Average SST March 2014

Image 2. Average SST September 2014

REFERENCES

http://www.remss.com/

Campbell, J. B. (2002). Introduction to remote sensing. New York [etc.] : Guilford Press. Retrieved from http://cataleg.uab.cat/record=b1622832~S1*cat

Gaiser, P. W., Member, S., Germain, K. M. S., Member, S., Twarog, E. M., Poe, G. A., Member, S. (2004). The WindSat Spaceborne Polarimetric Microwave Radiometer : Sensor Description and Early Orbit Performance, 42(11), 2347–2361.